The Hybrid Automatic Repeated Request (HARQ) mechanism plays a critical role in ensuring accurate reception of a transmission signal in an LTE communication system, and a User Equipment (UE) may receive an acknowledgement (ACK) signal and a negative acknowledgement (NACK) signal in an HARP procedure, where new data transmission is performed if an ACK signal is received, and data retransmission is performed if an NACK signal is received. In the current 3GPP LTE system, there are generally two ways to signal an ACK/NACK (also abbreviated as an A/N) to a UE: one is to use a Physical Hybrid-ARQ Indicator Channel (PHICH), and the other is to use a New Data Indicator (NDI) signal in a Physical Downlink Control Channel (PDCCH). Although a UE can always use an NDI in a Downlink Control Indicator (DCI) to recognize an A/N signal, the overhead of an uplink (UL) grant upon each transmission can not be negligible. In contrast, an A/N signal can be transmitted to a UE over the PHICH at a much lower overhead.
There are a greatly increased capacity of Physical Uplink Shared Channels (PUSCHs) and also a larger number of N/A signals over the PHICH in a Multi-User Multi-Input Multi-Output (MU-MIMO) scenario and a scenario of Coordinated Multi-Point (CoMP) with a shared cell ID. Particularly the greatly increased number of PUSCHs sharing the same radio frequency resource may incur a conflicting PHICH resource determined jointly by a starting Physical Resource Block (PRB) index of a PUSCH and a configured cyclic shift of a user-specific reference signal (DM-RS) according to a current PUSCH-and-PHICH association rule. This kind of collision may possibly cause mis-detection of an A/N signal by a UE.
The current PHICH has also become a bottleneck in a heterogeneous network particularly when Cell Range Expansion (CRE) is used. In this case, the PHICH will either suffer from more interference of another cell or cells or be blanked out in an Almost Blank Sub-frame (ABS). Thus there may be a greatly increased error probability of a transmitted A/N signal, and even an A/N feedback may be unavailable for some PUSCH transmission.